Preparation of a synthetic lubricating oil via a disproportionation reaction



United States Patent U.S. Cl. 260-672 5 Claims ABSTRACT OF THE DISCLOSURE A low pour point, high viscosity index synthetic lubricating oil, which is 1,3,5tri-n-alkylbenzene, is obtained in high yields by the disproportionation of mono-n-alkylbenzene in which the alkyl group has 6 to 9 carbon atoms, at selected operating conditions and with aluminum chloride catalyst. Each alkyl group of the 1,3,5-tri-n-alkylbenzene likewise contains 6 to 9 carbon atoms.

BACKGROUND OF THE INVENTION This invention relates to a process for producing low pour point, high viscosity index synthetic lubricating oils by the disproportionation of mono-n-alkylbenzenes. More particularly, this invention relates to the high yield production of certain 1,3,5-tri-n-alkylbenzenes whose physical properties are such that they can be used as a synthetic lubricating oil. Furthermore, accompanying the high yields of the desired product is the complete avoidance of the production of undesirable by-products defined hereinafter.

It is well known that n-alkylbenzenes, where the alkyl group contains 1 to 4 carbon atoms, will disproportionate to benzene, di-n-alkylbenzene and tri-n-alkylbenzene in the presence of Lewis acid-type catalysts such as AlBr or AlC1 or HF:BF It is further known that the rate of disproportionation and product distribution are a function of temperature and moles of catalyst to moles of reactant ratios. For example, U.S. Pat. 2,773,109 relating to the disproportionation of ethylbenzene With HFzBF shows 8 mole percent yield of 1,3,5-triethylbenzene at 50 C. while at 80 C. a 23 mole percent yield of 1,3,5-triethylbenzene is obtained. However, when the number of carbon atoms in the alkyl chain attached to the benzene is increased from two as in ethyl to three or four as in n-propyl or n-butyl, yields of the 1,3,5- tri-n-alkylbenzene decline while yields of undesirable byproducts, such as bicyclics and hydrocarbons boiling at a temperatuer higher than the desired tri-n-alkylbenzene increase. For example, U.S. Pat. 2,753,384 relating to the disproportionation of n-propylbenzene with HF:BF shows no yield of l,3,5-tri-n-propylbenzene at 5 C., while at 103 C. a yield of 13 mole percent of 1,3,5-tri-n-propylbenzene and of mole percent of undesirable .byproducts is shown. If 1,3,5-tri-n-butylbenzene is desired, undesirable by-product yields become even higher. This is shown also in U.S. Pat. 2,753,384 by an example wherein n-butylbenzene, at 103 C. and with HFzBF, is shown to disproportionate to 9 mole percent of 1,3,5- tri-n-butylbenzene and mole percent of undesirable byproducts. In the foregoing n-propylbenzene and n-butylbenzene examples, catalyst concentrations were similar and reaction times were the same.

Similar results have been obtained using aluminum chloride to disproportionate n-alkylbenzenes containing up to 4 carbon atoms in the alkyl group. Much of the work with n-propylbenzene is briefly reported in JACS, 76, 786787 (1954). In addition, this article reports experimental data on the disproportionation of n-butylbenzene using aluminum chloride catalyst. In this work n-butylbenzene, heated with 20 percent by weight of aluminum chloride for three hours at C., yielded 11.9 mole percent of undesirable by-products and no 1,3,S-tri-n-butylbenzene.

Attempts to disproportionate higher n-alkylbenzenes, such as n-decylbenzene to l,3,5-tri-n-decylbenzene, have been unsuccessful. For example, only 1,3-di-n-decylbenzene and some 1,2-di-n-decylbenzene were prepared by disproportionation of n-decylbenzene by contacting the n-decylbenzene with aluminum chloride at 25 C. for 14 days. The previous experiment was repeated but with the temperature at 100 C.; however, reactions other than disproportionation took place. (S. G. Clark Thesis (API Project 42), The Synthesis and Properties of Some High Molecular Weight Polyalkylbenzenes, Alkylphenanthrenes and Their Hydrogenated Analogs, The Penn State University, 1958.)

The previously discussed disproportionation work has been limited to tri-n-alkylbenzenes not suitable as a lubricating oil. The lower n-alkylbenzenes such as n-butylbenzene gives a relatively low molecular weight 1,3,5- tri-n-butylbenzene containing only 18 carbon atoms. If the disproportionation of n-decylbenzene would yield 1,3,5- tri-n-decylbenzene, the latter would contain 36 carbon atoms. Now the American Society for Testing Materials (ASTM) states that a hydrocarbon lubricating oil should contain from about 20 to about 34 carbon atoms. (Symposium on Composition of Petroleum Oils, Determination and Evaluation ASTM Special Technical Publication No. 224, ASTM.) Thus both the 1,3,5-tri-n-butylbenzene and 1,3,5-tri-n-decylbenzene with 18 and 36 carbon atoms, respectively, are outside the desired carbon atom range as recommended by the ASTM for hydrocarbon lubricating oils.

Contrary to expectations of low 1,3,5-tri-n-alkylbenzene yields and high undesirable by-product yields based on the previously discussed art it has now been found that, by the use of this invention, high yields of the desired 1,3,5-tri-n-alkylbenzenes can be obtained while avoiding the formation of unwanted by-products. In addition, the desired l,3,5-tri-n-alkylbenzenes have been found to have physical properties making them useful as synthetic lubricating oils.

SUMMARY OF THE INVENTION The invention resides in a process for producing a synthetic lubricating oil wherein mono-n-alkylbenzene, where the alkyl groups contains 6 to 9 carbon atoms, is disproportionated to 1,3,5-tri-n-alkylbenzene which is separated from the reaction mixture as the desired product. The process utliizes selected temperatures, type andconcentration of catalyst which produce the desired synthetic lubricating oil in high yields while avoiding the production of undesirable by-products. The resulting 1,3,5-tri-n-alkyl benzenes have desirable properties for use as lubricating oils including ASTM viscosity indexes as high as 149 and pour points below 100 C.

The reaction involved can be depicted by the following equation:

r r f Al on catalyst A R- R -R wherein R is n-hexyl or n-heptyl or n-octyl or n-nonyl. The above 1,3,5-tri-n-alkylbenzene is the desired product while the 1,3-di-n-alkylbenzene and benzene are coproducts. Any hydrocarbon other than those shown above are undesirable by-products.

3 DESCRIPTION OF THE INVENTION The n-alkylbenzenes used as reactants in this invention may be prepared by the telomerization reactions described in U.S. Pat. 3,206,519. Another way to prepare these nalkylbenzenes is by a Friedel-Crafts acylation followed by a Wolfi-Kishner reduction.

For the present purpose of disproportionating these nalkylbenzenes only aluminum chloride was found to be satisfactory for obtaining high yields of the desired 1,3,5- tri-n-alkylbenzenes. This is contrary to the general belief that the Lewis acid-type catalysts: AlBr AlCl and HF :BF are approximately equivalent as catalysts for disproportionation reactions.

The temperature at which the process of this invention is carried out not only determines yield of the desired 1,3,5-tri-n-alkylbenzenes but also determines the amount of the undesired by-products. Reactions, other than disproportionation, impose an upper temperature limit of about 80 C. on the n-alkyl transfer process, and it is generally desirable that the temperature does not exceed 60 C. The mobility of the n-alkyl group imposes a lower temperature limit of about C. but it is more desirable to operate at a temperature above C. For example, high yields of 1,3,5-tri-n-heptylbenzene are obtainable at C. Thus, while this invention can operate in a temperature range of about 10 C. to about 80 C., the pretferred temperature range is from about 30 C. to about C.

The process requires the presence of at least an amount of aluminum chloride sufiicient to cause the disproportionation reaction to take place. While amounts of AlCl as small as 0.01 mole per mole of n-alkylbenzene will cause disproportionation to take place, it is desirable to operate with about 0.3 to about 0.7 mole of A101 per mole of n-alkylbenzene. However, more AlCl can be used without detrimental eifect and even as much as 3.0 moles per mole of reactant may be used if desired.

The contacting time has an important effect on the course of the disproportionation reactions. At least sufficient time must be provided at the particular temperature of operation in order to obtain an appreciable amount of disproportionation products. As the contacting time is increased, at a constant temperature, the amount of disproportionation product increases. The disproportionation reaction appears to produce 1,3-di-n-alkylbenzene as the first product. Dependent upon the temperature, a finite period of time elapses between the appearance of detectable amounts of the 1,3-di-n-alkylbenzene product. The higher the temperature of the operation the shorter prolonged contacting times the reaction product mixture contains the 1,3,5-tri-n-alkylbenzene as the predominant disportionation reaction product. However, at prolonged contacting times at high temperatures reactions other than disproportionation take place at the expense of the 1,3,5- tri-n-alkylbenzene and the yield of desired product decreases.

The contacting time at a given temperature can be decreased by removing the benzene as it appears. The separated co-product benzene can be converted into n-alkyL benzene and recycled to the reaction zone.

While the reaction with aluminum chloride can be carried out at atmospheric pressure, other pressues can be used. The selection of pressure depends on whether the benzene is removed during the reaction and other related engineering factors.

The physical properties of the 1,3,5-tri-n-alkylbenzenes prepared by this process are shown in Table I.

Melting point, Pour point, F...

1 In centistokes at 100 F.

2 In centistokes at 210 F.

For comparison, automotive petroleum lubricating oils with additives will have a viscosity index ranging from about 90 to about 140 and pour points ranging from 35 F. to 0 F.; turbine oils with additives will have a viscosity index ranging from about 100 to 109 and pour points ranging from 0 F. to 10 F. Additional representative specifications for these and other kinds of lubricating oils can be found in Kirk and Othmer Encyclo pedia of Chemical Technology (2nd Ed., vol. 12, pp. 556667).

The data in Table II illustrate the advantage of the invention. In Runs 1 to 8 the catalyst is aluminum chloride. These runs were carried out in a flask equipped with a magnetic stirrer, condensers and drying tube. At the end of these runs the reaction mixture was poured on ice and a little dilute HCl was added. The mixture was then taken up in ether, dried and distilled. Identification of products and quantities thereof were determined by vapor phase chromatography, boiling points, mass spectroscopy and infrared analysis.

Actual yields of experiment in mole percent: benzene 40.6; n-hepthylbenzene 34.2;

1,3-di-n-heptylbenzene 9.4; 1,3,5-tri-n-heptylbenzene 15.8.

is the time before the appearance of an appreciable amount of the 1,3,5-tri-n-alkylbenzene.

With increasing contacting time, at constant temperature the amount of 1,3,5-tri-n-alkylbenzene gradually increases at the expense of the 1,3-di-n-alkylbenzene formed. Gradually the amount of the 1,3,5-tri-n-alkylbenzene increases and eventually the 1,3,5-tri-n-alkylbenzene continues to increase with the simultaneous disappearance of Percent of 1,3,5-tri-n-alkylbenzene in polyalkylated product in Table II means the moles of the 1,3,5-tri-n-alkylbenzene divided by the sum of the moles of 1,3,5-tri-nalkylbenzene plus the moles of 1,3-di-n-alkylbenzene times one hundred.

In Runs 1, 2 and 3 attempts to disproportionate namylbenzene to 1,3,5-tri-n-amylbenzene were unsuccess ful despite reaction contacting periods up to 18 hours or the 1,3-di-n-alkylbenzene. At higher temperatures and reaction temperatures as high as C. However in Runs 4, 5, 6 and 7, wherein the n-alkyl group of the n-alkylbenzene reactant contained 6, 7 or 8 carbon atoms, yields as high as 62.8% of the desired 1,3,5-tri-n-alkylbenzene were obtained. Although not shown, a similar yield as in Run 4 was obtained when using n-nonylbenzene as the reactant. Attempts to disproportionate n-dodecylbenzene to 1,3,5-tri-n-do-decylbenzene were unsuccessful as shown in Run 8.

Comparison of Runs 4, 6 and 7 indicate the influence of temperature on the yield of the desired 1,3,5-tri-n-alkylbenzene. In Run 4 at room temperature and with 0.5 mole of aluminum chloride per mole of n-hexylbenzene only 15.4 mole percent of the polyalkylated product was the wanted 1,3,5-tri-n-hexylbenzene. In Run 6 with a similar catalyst concentration but with n-heptylbenzene as the reactant and a higher temperature of 40 C., some 62.8 mole percent of the polyalkylated product was the desired 1,3,5-tri-n-heptylbenzene. Yet, in Run 7 using the lower room temperature with a similar catalyst concentration and n-octylbenzene as a reactant only 23.7 percent of the polyalkylated product was 1,3,5-tri-n-octylbenzene.

In Run 6 at 40 C. all the aluminum chloride was dissolved in the hydrocarbon; this was indicated by the existence of a homogeneous or one-phase mixture. The other seven runs shown in Table II were at temperatures at which all of the aluminum chloride was not dissolved in the hydrocarbon; this was indicated in these runs by the existence of two-phase mixtures. Therefore in Run 6 a high yield was obtained of the desired 1,3,5-tri-n-heptyl compared to Run 4 because the temperature of 40 C. was high enough to dissolve all the aluminum chloride in the hydrocarbon whereas in Run 4 the room temperature was not high enough to dissolve all the aluminum chloride in the hydrocarbon. Thus while in Runs 4 and 6 the ratio of the amounts of catalyst to the amount of the reactant in the reaction vessel was the same, the amount of catalyst actually in contact with the reactant was substantially greater in Run 6.

Two additional runs indicating the non-equivalence of aluminum chloride and HF:BF are shown in Table III. These comparative HF:BF runs were made in a small bomb shaken in a thermostated oil bath. As before, identification of products and quantities thereof are determined by vapor phase chromatography, boiling points,

In Run with 0.25 mole of aluminum chloride per mole of n-heptylbenzene a yield of 13.3% of the desired product was obtained after only 90 minutes. Yet in Run 9 with 1.0 mole of BF per mole of n-heptylbenzene no l,3,5-tri-n heptylbenzene was found after 4200 minutes.

In Run 10 the catalyst was lowered to 0.5 mole per mole of reactant and again no 1,3,5-tri-n-heptylbenzene was found. Thus while the catalyst concentration in Run 10 compared to Run 9 was reduced by no change in the yield of the desired 1,3,5-tri-n-heptylbenzene was found. Runs 9 and 10 indicate that the production of 1,3,5-tri-n-heptylben2ene is insensitive to changes in B1 catalyst concentration at these temperatures. Therefore, no run was made with 0.25 mole of HFZBFg catalyst per mole of reactant.

From the foregoing it can be seen that this process provides a way of making in high yields 1,3,5-tri-nhexylbenzene or 1,3,5-tri-n-heptylbenzene or 1,3,5-tri-noctylbenzene or 1,3,5-trin-nonylbenzene for use as high viscosity index and low pour point lubricating oils either individually or mixed together in various proportions. The surprisingly high yields of the desired 1,3,5-tri-nalkylbenzene with no yields of undesirable by-products came about by using aluminum chloride catalyst and a narrow range of operating conditions.

I claim:

1. Process for producing a high viscosity index, low pour point, synthetic lubricating oil which comprises contacting an n-alkylbenzene in which the alkyl group has 6 to 9 carbon atoms with aluminum chloride catalyst at a disproportionation temperature of at least 10 C., continuing such contacting until a substantial proportion of 1,3,5-tri-n-alkylbenzene has been formed and separating said tri-n-alkylbenzene from the reaction mixture.

2. Process according to claim 1 wherein the temperature is less than C.

3. Process according to claim 1 wherein the temperature is in the range of about 30 C. to about 60 C.

4. Process according to claim 1 wherein the molar ratio of aluminum chloride catalyst to reactant is between about 0.01 and 3.0. r

5. Process according to claim 1 wherein the molar ratio of aluminum chloride catalyst to reactant is between mass spectroscopy and infrared analysis. 45 about 0.3 and 0.7.

TABLE III Percent of 1,3,5- Moles of Catalyst, and tri-n-heptylcatalyst per reactant conbenzene in mole of N- taeting time, polyalkylated Run Catalyst heptylbenzene Temp., 0. minutes product 5 A1013 0. 25 25 13.3 9 HFzBFa l 1.00 28 4, 200 0 10 HFZBFS 1 0. 50 28 4, 200 0 1 Excess HF used, at least 3 moles of HF per mole of reactant.

References Cited UNITED STATES PATENTS 2,753,384 7/1956 Lien et al. 260-668 3,173,965 3/1965 Pappas et al 260-667 3,392,206 7/ 1968 Hurley et al. 260671 3,398,206 8/1968 Strohmeyer 26067l DELBERT E. GANTZ, Primary Examiner G. E. SCHMITKONS, Assistant Examiner U.S. Cl. X.R. 

